Your basal metabolic rate is what your body uses at complete rest. Multiply it by an activity factor and you get maintenance — what keeps you where you are. A target is maintenance plus or minus a deficit.
The one rule enforced in code rather than left to small print: the target never goes below a safe floor. If a full deficit would take it under, the tool holds it at the floor and tells you it did. A calculator that quietly returns a smaller deficit than the one you asked for is worse than one that argues with you.
Because a full 500 kcal deficit would have taken it below a floor the tool will not go under — 1,200 kcal a day on the female variant, 1,500 on the male. The target is held at that floor and the page says so, rather than quietly handing you a smaller deficit than the one you asked for. Eating below those figures is something to do with a doctor, not a calculator.
Because that is honestly what it is. The Mifflin-St Jeor equation was fitted with two constants, +5 and −161, and the tool has to pick one. That is a limitation of the equation, not a statement about you. If neither fits your situation, the figure will be approximate — as it is for everyone — and a dietitian can do better than any formula.
It is an estimate from an equation fitted to a population, and individuals vary by a few hundred calories either way. It knows nothing about your body composition, your thyroid, your medication or your sleep. Treat it as a starting point, weigh yourself over a few weeks, and adjust based on what actually happens.
A deficit of about 500 a day works out to roughly half a kilogram a week, which is the rate most guidance treats as sustainable. Faster is not better — past that point, more of what comes off is muscle rather than fat, and the diet is harder to hold.
It is a balanced starting point — 30% protein, 40% carbohydrate, 30% fat — not a prescription. Grams differ from calories because fat carries 9 calories a gram against 4 for protein and carbohydrate, which is why the fat number looks small.
Chosen over Harris-Benedict: it is the more accurate of the two on modern populations.
Most people overestimate this. If in doubt, pick the level below the one you were about to.
Commonly cited as the point below which a diet should be medically supervised. It is a guardrail this tool respects, not a recommendation, and not a substitute for asking a doctor. Where maintenance is already under the floor, no deficit is applied at all — the guardrail raises a target, it never tells anyone to eat more than they need.
A general reference figure, not a medical assessment or a diet plan. It cannot know your body composition, your medical history or your medication. Speak to a doctor or a dietitian before making a real change, and never eat below the floor shown here without supervision. Nothing you type here is sent to our servers — the calculation runs entirely in your browser.
